2D graphene-assisted low-cost metal (Ag, Cu, Fe, or Ni)-doped TiO2 nanowire architectures for enhanced hydrogen generation

Abstract

Without assistance from expensive noble metals, we report optimal conditions for upgraded H2 generation using 2D graphene (GP)-assisted low-cost metal (Ag, Cu, Fe, or Ni)-doped TiO2 nanowire (GP/M/TNW) architectures. To examine the optimal conditions for H2 generation, photocatalytic tests using the GP/M/TNW catalysts were performed under various conditions based on the types and amounts of metal and sacrificial reagent. In addition, the effect of the amount of GP in graphene-assisted TiO2 nanowire (GP/TNW) catalysts on H2 generation yields was investigated. Solar light-driven GP/M/TNW nanostructures with upgraded photocatalytic performance were successfully prepared using a hydrothermal method with post-thermal treatment, as evidenced by their physicochemical characteristics. With a H2 yield of 22 mmol g−1 after 5 h illumination, GP/Cu/TNW samples exhibited a substantially higher photocatalytic efficiency for H2 generation than three reference catalysts (TiO2, TNW, and GP/TNW), which is attributed to both increased visible light absorption and efficient charge separation. The H2 generation yields of GP/M/TNW samples were in the order of: GP/Cu/TNW > GP/Ni/TNW > GP/Ag/TNW > GP/Fe/TNW. A GP content of 10% and a Cu loading of 10% were optimal for the synthesis of GP/TNW and GP/Cu/TNW catalysts, respectively. The optimal sacrificial reagent type and amount for H2 generation using GP/Cu/TNW catalysts were 20% (v/v) methanol. Moreover, the photocatalytic yields of H2 via a GP/Cu/TNW catalyst did not vary significantly over three successive experimental runs. A thermodynamically-suitable reaction mechanism for H2 generation over GP/Cu/TNW heterostructures was proposed.